title: Factor VIII clotting antigen (VIIICAg) in haemophilia measured by two immunoradiometric assays (IRMA) using different antibodies, and the measurement of inhibitors to procoagulant factor VIII (VIIIC) by IRMA.
abstract: Factor VIII clotting antigen (VIIICAg) was measured by immunoradiometric assay (IRMA) using two different antibodies. Both antibodies arose in polytransfused severe haemophiliacs and had similar titres against VIIIC. In 12 normal plasmas there was no significant difference in VIIICAg values obtained (VIIICAg (AbI) = VIIICAg (AbII)). In the majority of 15 severe haemophiliacs tested VIIICAg was undetectable by both antibodies. In 28 mild to moderate haemophiliacs VIIICAg (AbII) was significantly greater than VIIICAg (AbI) (P less than 0.01) suggesting different antigenic determinants. The difference, however, was small and does not affect diagnosis of haemophilia. A modified IRMA has been used to measure anti VIIIC inhibitors by competition of the inhibitor with 125I labelled VIIICAg antibodies for common antigenic determinants. Using an inhibitor of 225 Bethesda units as a standard, results by IRMA of inhibitors in severe haemophiliacs have been similar to those obtained by clotting assay, but with a sensitivity of 0.01 u/ml suggesting the possible use in the detection of weak inhibitors.
mesh_terms: D000906:Antibodies / Q000032:analysis; D000941:Antigens / Q000032:analysis*; D001667:Binding, Competitive; D005169:Factor VIII / Q000032:analysis / Q000276:immunology*; D006467:Hemophilia A / Q000276:immunology*; D006801:Humans; D011863:Radioimmunoassay
chemical_list: D000906:Antibodies; D000941:Antigens; D005169:Factor VIII